Optical communication devices are used in a variety of applications including, but certainly not limited to self powered identification and data tags, infrared wireless and fiber optic transceivers, and solar powered sensors. Optical identification and data tags have certain advantages over Radio Frequency Identification (RFID) and data tags. Solar powered sensors are currently large and expensive, which limits their application.
Self powered radio frequency identification (RFID) tags have been used for years for identifying items with a unique identification number that can be read electronically with a special powered reading device. The penetration into the marketplace is growing but has been limited by the cost of the tag, which includes an antennae that is necessary for RF communication.
The Hitachi Mu-Chip is an example state of the art RFID device. Although the device measures only 2.5 mm×1.5 mm, it requires the antennae, which measures 54 mm×1.5 mm. Additionally the chip must be mounted and connected to the antennae, which increases cost and reduces reliability. Other well known limitations of RFID tags include disturbances due to metal, water, and electromagnetic interference (EMI), and cross talk between tags. In harsh environments and along conveyor belts, for instance, with closely spaced tagged items, RFID tags can be unreliable.
To work in harsh environments, a Swedish company, Scirocco AB, has developed Infrared Identification (IRID) tags, which contain an energy converter block to power the tag from infrared or visible light, and an infrared transmitter block which sends the contents of the ID register when the tag is powered. The Scirocco data tags additionally provide some memory and an infrared detector block to enable data tags to receive and store data in non-volatile memory. Additional information on the Scirocco tags and system are described in U.S. Published Patent Application No. US 2006/0164291.
The Scirocco system provides an identification solution that overcomes certain limitations of RFID systems with respect to metal shielding, water, EMI, and interference, which is appropriate for relatively low volume target applications. For very high volume applications, such as consumer package tracking, smart cards, keyless entry, retail inventory identification, etc. the cost may be prohibitive. The Scirocco identification tags have separate power supply (energizer) and infrared transmitter circuits, and the data tags additionally contain separate infrared detector circuits, which increase component count and cost.
The energizer circuitry contains an array of silicon diodes with at least two sets of diodes connected in series to produce sufficient voltage and current to power the tag. The transmitter contains an infrared LED and some driver circuitry. The infrared detector circuitry contains a reverse biased silicon photodiode connected to an amplifier circuit. All this circuitry increases the total cost of components in the tags and increases the power consumption, which further increases the cost and/or reduces communication distance.
The most common protocol for infrared wireless communication is Infrared Data Association (IRDA), which was developed in the early 1990's for communication between a computer and its peripherals. The Vishay TFDU4101 IRDA transceiver implements the physical layer of this protocol stack. The TFDU4101 package is called a “Babyface” since it has two separate transparent domes for transmitting and receiving infrared light. Under one dome is an LED for transmitting and under the other dome is a silicon photodiode for receiving. The associated LED driver and photodiode receiver circuitry is implemented in one or two silicon chips.
An increasingly popular protocol for optical networking in automobiles is called Media Oriented System Transport (MOST), which was introduced in the late 1990's to enable multimedia components in a car to communicate. One of the physical layers for MOST is a ring of unidirectional point-to-point optical links using plastic optical fiber (POF). Each optical link has a fiber optic transmitting module at one end of the POF and a fiber optic receiving module at the other end.
One supplier of opto-electrical converters useful for MOST is Avago. Their optical transmitter contains an LED and a driver IC, while the receiver contains a photodiode and receiver IC. Data flows in one direction through the optical link from one node to the next. Bi-directional communication is essentially accomplished by connecting all devices in a uni-directional ring topology, which works fine unless one link or one node is not functioning properly. If one device or one link goes down, bi-directional communication is not possible.
Sensing of signals such as temperature, pressure, strain, acceleration, moisture, etc is commonly needed in locations that are costly to power and communicate with using wires. Consequently, remote sensors are available that include batteries and some form of wireless communication. The NPX1 tire pressure sensor from GE includes a Lithium Ion battery and a UHF transmitter that enables the module to reside inside a rotating tire.
In some cases, the sensors include solar cells that recharge the battery from sunlight or ambient light, such as certain strain gauge devices available from MicroStrain. Such devices may be placed, for example, at critical locations on a bridge to monitor strain on the bridge, and to communicate data to a reading device through a wireless RF link. Such sensor devices are frequently very large and expensive.
There exists a need to overcome problems existing in prior solutions and to provide a more efficient and cost effective solution for optical communications and identification devices.